The Prime Directive, also known as Starfleet General Order 1 or the Non-Interference Directive, was the embodiment of one of Starfleet's most important ethical principles: noninterference with other cultures and civilizations. At its core was the philosophical concept that covered personnel should refrain from interfering in the natural, unassisted, development of societies, even if such interference was well-intentioned. The Prime Directive was viewed as so fundamental to Starfleet that officers swore to uphold the Prime Directive, even at the cost of their own life or the lives of their crew. The "precursor" to the Prime Directive, though somewhat undefined, could be traced back to Captain Archer's and Phlox's ethical dilemma faced when encountering two species, one with a terminal genetic illness and the other without. They decided that interfering with the natural evolutionary course of these two species would go against the "directive" upon which they based their entire mission; to meet new species and attempt peaceful communications, not to "play God".
The fundamental principles were an important part of Earth Starfleet procedures as early as 2152, but it did not go into effect as a General Order until sometime after 2168.
- Star Trek Into Darkness (First appearance)